[ctml_writer] Fix handling of third body names containing parentheses

Replace the heuristic used to remove the third body terms from the
reactant and product lists to handle species names that include
parentheses.

interfaces/cython/cantera/ctml_writer.py

@@ -1400,7 +1400,7 @@ def clean_up_reactants_products(self):
             del self._p['m)']
         else:
             for r in list(self._r.keys()):
-                if r[-1] == ')' and r.find('(') < 0:
+                if r[-1] == ')' and r in self._p:
                     species = r[:-1]
                     if self._eff:
                         raise CTI_Error("In reaction '{0}', explcit third body "